1. Field of the Invention
The invention relates to indicia display devices and somewhat more particularly to a method of producing spacing elements for indicia display devices such as liquid crystal cells and to display devices utilizing such spacing elements.
2. Prior Art
Electro-optical display devices, such as liquid crystal cells are known, for example see U.S. Pat. No. 3,995,941 (which corresponds to German Offenlegungsschrift No. 2,254,940). In a series of such electro-optical devices, it is important to insure that the two carrier plates of a device maintain a spacing relative to one another which is as exact as possible. This requirement is especially critical for liquid crystal display devices (FKAs) because important liquid crystal indication characteristic data, such as for example, the switching behavior or the value of the threshhold voltage for an FKA is extremely dependant upon the thickness of the liquid crystal layer. Accordingly, spacing tolerances are particularly low when FKAs are operated in a multiplex method and/or with a so-called "bistability effect". In certain extreme present-day cases, spacing tolerances of about .+-.5%, thus fractions of a .mu.m are required.
In order to achieve such spacing precision, workers in the art have proposed numerous and widely diverse solutions. For example, in the earlier cited U.S. Pat. No. 3,995,941 it is proposed to include relatively small sized particles between carrier plates of an FKA. Such particles may comprise glass fibers, metal fibers, whisker crystals or the like. It is suggested that glass particles or fibers are preferred for the spacing function because they are thermally stable in an FKA environment and can readily be produced with a required diameter dimension which is exact to about .+-.10%. However, metal fibers would be even more accurate as to size because suitably thick metal filaments having thickness fluctuations of only about .+-.5% are actually available. Nevertheless, metallic spacing particles have, up until now, been unsuitable for use in FKAs, primarily because their thermal coefficient of expansion deviates too much from that of the other elements in an FKA and even more importantly because the ductility of a metal wire or filament prevents its desired reduction in size via an expenditure which is justifiable. Further, metal particles are electrically conductive and, for that reason alone, are only useful in a few special cases.